Researchers have found garlic supplements can cause a potentially harmful
side effect when combined with a type of medication used to treat HIV/AIDS.
Investigators from the National Institutes of Health (NIH) observed that garlic
supplements sharply reduced blood levels of the anti-HIV drug saquinavir. The
study results appear this week in an on-line edition of Clinical
Infectious Diseases.
"In the presence of garlic supplements, blood concentrations of saquinavir
decreased by about 50 percent among our study participants," explains the
study's senior co-author Judith Falloon, M.D., an AIDS clinical researcher at
the National Institute of Allergy and Infectious Diseases (NIAID). "We saw a
definite, prolonged interaction. The clear implication is that doctors and
patients should be cautious about using garlic supplements during HIV therapy,"
she says.
For the first 3 days of the study, nine healthy, HIV-negative volunteers
received doses of saquinavir, one of a class of drugs called protease inhibitors
that are effective at slowing the progression of HIV infection. The research
team drew samples from the volunteers' blood to measure their baseline levels of
saquinavir in the bloodstream.
Next, the volunteers took garlic caplets twice daily for 3 weeks. When the
researchers again analyzed blood samples, the average overall levels of
saquinavir had decreased 51 percent, and the average maximum concentrations had
fallen 54 percent.
Even after a 10-day "wash-out" period with no garlic supplements, when the
volunteers again used only the protease inhibitor for 3 days, their blood levels
of saquinavir still averaged about 35 percent lower than the expected baseline
amount.
The research paper's lead author is Stephen C. Piscitelli, Pharm.D., formerly
with the NIH Clinical Center Pharmacy Department and now the Associate Director
of Clinical Pharmacology at Tibotec-Virco. Noting that some dietary supplements
can cause detrimental interactions with medications, Dr. Piscitelli and his
colleagues set out to investigate the effects of a number of herbal therapies.
As Dr. Falloon explains, "We set out to learn more about these alternative
medicine products because there simply are not a lot of clinical data available
on them." In their first study, the team found a potentially dangerous
interaction between the herbal remedy St. John's wort and the protease inhibitor
indinavir.
Garlic became the next focus because of its reputation as a natural
cholesterol fighter, which has made it particularly popular for patients whose
cholesterol levels have risen due to a side effect from HIV medications. The
research team also suspected a strong possibility of a drug interaction because
both garlic and protease inhibitors share the same pathway into the body, a
metabolic route known as the CYP450 enzyme system. Exactly how garlic
supplements disrupt the uptake of saquinavir is still unclear.
Other questions remain as well, says Dr. Falloon. Usually, doctors prescribe
saquinavir to be taken together with several anti-HIV drugs, and it is unknown
how garlic supplements would affect such a combined drug regimen. "More research
is needed in this area, but it's clear from this study that any patient using
saquinavir as the sole protease inhibitor should avoid using garlic
supplements," says Dr. Falloon.
NIAID and the Warren Grant Magnuson Clinical Center are components of NIH.
NIAID supports basic and applied research to prevent, diagnose, and treat
infectious and immune-mediated illnesses, including HIV/AIDS and other sexually
transmitted diseases, tuberculosis, malaria, autoimmune disorders, asthma, and
allergies. The Clinical Center is the clinical research hospital for NIH.
Through clinical research, physicians and scientists translate laboratory
discoveries into better treatments, therapies, and interventions to improve the
Nation's health.
